The present invention relates to providing an apparatus, system and method of reducing and/or eliminating fugitive emissions from a service station underground storage tank.
Fuel is prepared to have a certain Reid Vapor Pressure (RVP) before being delivered to an underground storage tank at a service station for later dispensing into a vehicle. RVP is measure of a fuel""s volatility at a certain temperature and is a measurement of the rate at which fuel evaporates and emits volatile organic chemicals (VOCs), namely hydrocarbons (HCs). RVP is measured by measuring the pressure of fuel vapor at a temperature of 100 degrees Fahrenheit. The higher the RVP, the greater the tendency of the fuel to vaporize or evaporate. The RVP of fuel can be lowered by reducing the amount of a volatile liquid""s most volatile components, such as butane in gasoline fuel for example.
In a service station environment, fuel having a higher RVP, for example 14 pounds per square inch (Psi), is typically delivered during the winter months, whereas fuel having a lower RVP, for example 7 Psi, is typically delivered during the summer months. The reason that it is desirable to deliver fuel to a service station having a lower RVP during the summer months is that this can offset the effect of higher summer temperatures upon the volatility of the fuel, which in turn lowers emissions of VOCs. Emissions of VOCs cause product of ground level ozone and increased exhaust emissions from vehicles. During the winter months, it is desirable to provide fuel having a higher RVP, which ignites easier in colder temperatures.
In service stations employing Stage II vapor recovery systems, the vapor emanating from the vehicle tank during refueling is recovered and is returned to the underground storage tank. During the summer months, the vapor recovered and collected from the vehicle tank has a higher temperature than the underground storage tank. Therefore, the collected vapor shrinks in volume in the underground storage tank due to this temperature differential. It is also less likely for summer fuel, having a lower RVP, to evaporate in the underground storage tank and create vapor growth and therefore volume increase.
During the winter months, the vapor emanating from the vehicle tank collected and returned to the underground storage tank is lower in temperature than the underground storage tank. As a result of this temperature differential, the recovered vapor from the vehicle expands in volume when it enters the underground storage tank. Additionally, the vapor returned to the underground storage tank reacts with the higher RVP fuel in the underground storage tank and vapor growth occurs due to the high volatility of the fuel. This further increases vapor growth in the underground storage tank. If the pressure in the underground storage tank reaches a certain threshold level, a vent to atmosphere is opened to release this excess pressure so that the underground storage tank is not over-pressurized. This release of excess pressure causes vapors or VOCs to be released into the atmosphere thereby causing harm to the environment.
Therefore, a need exists to provide a system and method to keep vapors collected from a vehicle during refueling and resident in the underground storage tank from expanding in the underground storage tank to keep pressure from increasing and releasing VOCs to atmosphere.
The present invention relates to a vapor pressure equalizer system that cools vapors in the ullage of a volatile liquid storage tank to reduce the pressure inside the volatile liquid storage tank. Reduction of pressure in a volatile liquid storage tank makes it less likely that leaks will occur in the storage tank, and/or any pressure relief valve that is connected to the vent stack running to the ullage of the underground storage tank that is opened to release pressure will be opened and as a result, release volatile vapors into the atmosphere thereby harming the environment.
In a first embodiment, the volatile liquid storage tank holds fuel in an underground storage tank in a service station environment. The system is comprised of a conduit having an inlet port and an outlet port. A valve is connected inline to the conduit, and the valve has a valve inlet and a valve outlet. A pump and heat exchanger are connected inline to the conduit downstream of the valve outlet. An electronic controller is electrically coupled to the valve to control the opening of the valve, and the electronic controller is also electronically coupled to the pump to activate the pump. The electronic controller is adapted to open the valve and activate the pump to draw vapors from the ullage of the storage tank through the inlet port to pass the vapor through the heat exchanger to cool the vapor and return the cooled vapor through the outlet port to the ullage of the storage tank.
In another embodiment, the volatile liquid storage tank holds fuel in an underground storage tank in a service station environment as well. The system is like that of the first embodiment; however, the conduit is not open to the storage tank to draw in vapors from the ullage. Instead the conduit is a closed system and includes a radiator that is placed in the ullage of the storage tank. A cooling media is circulated through the conduit and the radiator, and the radiator cools the vapor in the ullage of the storage tank through heat exchange.
In another embodiment, the volatile liquid storage tank holds fuel in an underground storage tank in a service station environment as well. The system is like that of the first embodiment; however, the inlet and outlet of the conduit are connected to the vent stack instead of the ullage of the storage tank. This may be advantageous if placing additional holes for the inlet and outlet of the conduit to be placed in the underground storage tank is impractical or if the vapor pressure equalizer system is being added to an existing storage tank, which may be underground.
In another embodiment, the volatile liquid storage tank holds fuel in an underground storage tank in a service station environment as well. The conduit and heat exchanger system is placed between a fuel dispenser and the underground storage tank inline with the vapor return passage. As vapor is recovered by the fuel dispenser from a vehicle fuel tank during refueling, the electronic controller controls if the vapor is returned directly to the ullage of the underground storage tank or to the heat exchanger system first. If the electronic controller directs the vapor to the heat exchanger system, the vapors are cooled before being returned to the underground storage tank, thereby reducing the volume of vapors being returned and the temperature of the ullage, which may also reduce the volume of vapors already in the ullage of the underground storage tank.
Those skilled in the art will appreciate the scope of the present invention and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures.